Depending on the type of field you used for your upload element, there will be a few ways you can locate the documents your client attached to their template.

If it was a dataset element (which means the element on your template is connected to the profile) you'll be able to navigate to the page within the clients profile and locate any attachments here.  You can click on the attachment to view/download it.
 

You can also view a list of attachments on the engagement through the engagement details panel.